1. Field of the Invention
The present invention relates to a pneumatic tire, more particularly to an improved tread block structure being capable of improving road grip such as mud and snow grip of the tire and resistance to cracks and tear-off of the block.
2. Description of the Related Art
In heavy duty radial tires for trucks, construction vehicles and the like used on bad roads such as muddy or snowy roads, block patterns are widely used to provide a good road grip.
In the U.S. Pat. No. 6,000,451, such a block pattern is disclosed, wherein, as shown in FIG. 1, center blocks (Bc) which highly contribute to the traction, are provided on or near the tire equator with circumferentially opening V-shaped corners (J) instead of a circumferentially pointed outward corner. Such corners (J) make it possible to grip snowy and muddy roads effectively, whereby superior road grip such as traction and braking can be obtained. (Therefore, this pattern is also employed in the following embodiment of the present invention.)
In the center blocks (Bc), however, the rigidity decreases near the corners (J), and the deformation becomes larger near the corners than other part. As a result, from the middle stage to the last stage of the tread wear life, cracks are liable to occur at the corners (J), and in the worst cases, blocks (Bc) are torn off and the tread reinforcing belt is exposed. As a result, damages to the tire such as cord corrosion and cord rupture which make it impossible to retread the tire are caused.
It is therefore, an object of the present invention to provide a pneumatic tire having tread blocks provided with corners in which cracks starting from the corners are decreased to prevent the blocks from tearing off, without deteriorating the road grip.
According to the present invention, a pneumatic tire comprises a tread portion provided with blocks, each block provided with circumferentially opening V-shaped corners each defined between two corner walls intersecting each other,
in a cross section including the intersecting line K of the two corner walls and a normal line drawn normally to the tread face from a radially outer end of the intersecting line K, the intersecting line K comprising an upper slanting part KU and a lower normal part KL, the upper slanting part KU extending radially inwards from the tread face to a point P1 with an inclination angle xcex81 with respect to said normal line, and the lower normal part KL extending radially inwardly from the point P1 in substantially parallel to the normal line, and the depth Dl of the point P1 from the tread face being in a range of from 0.30 to 0.50 times the height H0 of the block.